The vehicular industry is increasingly adding more systems for providing safety-related features. Next phase automotive safety systems, collectively known as intelligent transportation system (ITS), rely on interactions among vehicles, as well as interactions between vehicles and infrastructure. Examples of features enabled by such interactions include, but are not limited to, hazardous location warning (e.g. reporting a hazard by one vehicle to another vehicle), green light optimized speed advisory (GLOSA) which provide speed advisories to vehicles based on a time duration before which a green light at a signalized intersection will change, motorcycle warnings, emergency vehicle warnings, road work warnings, traffic jam warnings, etc.
As the capabilities of such systems evolve, additionally complex safety applications that are more communication-intensive will be deployed. Further, such safety applications demand that such messages are delivered with a very high reliability and very low latency. While IEEE 802.11p or Rel-14 LTE supports such messaging, it has significant limitations with respect to reliability and latency, particularly when vehicle density is high. Furthermore, as system capabilities and use-cases evolve, the required data rates are expected to be much higher than that which IEEE 802.11p or Rel-14 LTE can support.
In order to meet latency requirements, the communication path used in IEEE 802.11p is generally a direct vehicle-to-vehicle communication link. On the other hand, in order to meet reliability requirements on the vehicle-to-vehicle link, various techniques are employed such as low order modulation, low code rate, retransmissions, etc. However, these techniques generally result in inefficient operation and lower system capacity. There is thus a need for techniques that utilize both vehicle-to-vehicle direct communication and infrastructure-to-vehicle communication to overcome some of these issues.